Dexmedetomidine is a new selective and potent alpha-2 agonist. It has centrally acting anesthetic properties. It has been known that intrathecal addition of alpha-2 adrenergic agents result in prolongation of the duration of the sensory and motor blockade induced by hyperbaric bupivacaine. But the effects of intravenous dexmedetomidine on the spinal block was not evaluated. The aim of study is to assess the effect of intravenous dexmedetomidine on the low-dose spinal anesthesia for the transurethral surgery.